Gas manifold for uniform gas distribution and photochemistry

ABSTRACT

The invention provides a system for providing a flow of a short-lived, reactive process gas species into an RTP chamber without creating ionic species. An RTP chamber includes a transparent quartz window assembly. The window assembly has a first pane facing a wafer inside the RTP chamber. A second pane is positioned adjacent a heat lamp array on the outside of the RTP chamber. A window side wall joins the first and second panes at their peripheral edges to provide an internal chamber therebetween. A plurality of channels extend through the first pane from the internal chamber to the inside of the RTP chamber. A port communicates between the internal chamber and a process gas source. The window assembly also includes a reflective surface facing the internal chamber. An ultraviolet light source is positioned to illuminate process gas flowing through the window assembly with ultraviolet light such that the ultraviolet light alters the chemistry of the process gas. A process using the reactive gas species can be turned on and off quickly by turning on and off the ultraviolet light.

CROSS-REFERENCE TO RELATED APPLICATION

This is a divisional of application Ser. No. 09/087,489, files May 29,1998 now U.S. Pat. No. 6,187,133.

BACKGROUND OF THE INVENTION

The invention relates to a method and apparatus for producingshort-lived reactive species in a rapid thermal processing (RTP) system.

RTP systems are employed in semiconductor chip fabrication to create,chemically alter, or etch surface structures on semiconductor wafers. Inone type of system, an RTP chamber includes a gas manifold, sometimesreferred to as a gas showerhead, positioned above the surface of thewafer to provide a flow of a process gas to the wafer surface. Radiantenergy from a heat lamp array passes through the manifold, which can bemade of transparent quartz, to heat the wafer during processing. Spentprocess gas can be pumped out through a vacuum port of the chamber.

Completely replacing one process gas with another one typically takesseveral minutes with a conventional gas showerhead system. For thisreason, it is very difficult to rapidly switch from one type of processto another at the surface of the wafer, such as is desirable in creatingvery thin layers or structures on the wafer surface. Some RTP processesemploy highly reactive species, such as atomic species. In conventionalsystems, these species are created outside the RTP system, for example,with an electric discharge. The reactive species created by such methodsmust travel long paths to reach the wafer with conventional showerheadsystems. Atomic species can also be created with an electric dischargewithin the RTP chamber, but employing an electric discharge close to thewafer surface also creates a plasma that can be detrimental to thesemiconductor devices being formed on the wafer.

SUMMARY OF THE INVENTION

According to one aspect of the invention, an apparatus for producing areactive gas in a processing chamber includes a gas manifold that haswalls providing an internal chamber. A first wall includes a side facinga work piece, another side facing the internal chamber, and a pluralityof channels extending from the internal chamber to the side facing thework piece. The gas manifold also includes a port for coupling a gassource to the internal chamber such that a gas flowing into the internalchamber through the port flows out through the channels toward a surfaceof the work piece. An ultraviolet light source is structured andarranged to illuminate the gas flowing through the gas manifold foraltering the chemistry of the gas. The gas manifold can include areflective surface facing the internal chamber for reflecting theultraviolet light.

The walls of the gas manifold can comprise a window formed oftransparent quartz. A second wall can be arranged spaced apart from thefirst wall and adjacent a heat lamp array, with a side wall joining thefirst and second walls at their peripheral edges. The ultraviolet lightsource is structured and arranged to illuminate the gas in the internalchamber through a window region in the side wall, the ultraviolet lightbeing directed between the first and second walls.

According to another aspect of the invention, a rapid thermal processingchamber for processing a semiconductor wafer positioned within theprocessing chamber includes a transparent window. The window includes afirst pane facing the wafer inside the processing chamber, a second panebeing adjacent a heat lamp array on the outside of the processingchamber, a window side wall joining the first and second panes at theirperipheral edges to provide an internal chamber therebetween, aplurality of channels extending through the first pane from the internalchamber to the inside of the processing chamber, a port communicatingbetween the internal chamber and a process gas source, and a reflectivesurface facing the internal chamber. An ultraviolet light source ispositioned to illuminate process gas flowing through the window withultraviolet light such that the ultraviolet light alters the chemistryof the process gas. The ultraviolet light source directs the ultravioletlight substantially parallel to the first and second panes, and into theinternal chamber such that the ultraviolet light reflects from thereflective surface in a plurality of different directions within theinternal chamber.

In both the gas manifold and the processing chamber, the ultravioletlight source can include one of an ultraviolet lamp, a mercury dischargelamp, and a ultraviolet laser. The ultraviolet light source can alsoinclude a controller for turning the illumination on and off, andoptical elements directing the ultraviolet light from the ultravioletlight source to pass through a transparent window region of the windowside wall into the internal chamber. If the ultraviolet light source isa laser, the controller can include a tuner capable of changing thewavelength of the ultraviolet light provided by the laser.

According to yet another aspect of the invention, a method of processinga semiconductor wafer in a semiconductor process chamber includes thesteps of providing a flow of a precursor gas species into a gasmanifold, illuminating the precursor gas species in the gas manifoldwith ultraviolet light, wherein the ultraviolet light interacts with theprecursor gas species to create a product gas species, and flowing theproduct gas species through a plurality of apertures in the manifoldtowards the wafer in the processing chamber. The illuminating caninclude reflecting the ultraviolet light off a reflective surface of themanifold so that the ultraviolet light passes through the gas manifoldmore than once, thereby increasing the interaction with the precursorgas species. The processing can be controlled by controlling theilluminating.

The gas manifold can include a transparent window, and the method canfurther include the step of heating the wafer by shining radiant energyfrom a heat lamp array through the window.

The product gas species, which is non-ionic and will typically be morereactive than the precursor gas species, can include nitric oxide,ozone, an atomic species, or any other gas species that can be producedby illuminating a precursor gas species with ultraviolet light. Theproduct gas species can be a reactive gas species having a half-life ofabout a minute or less.

According to still another aspect of the invention, a method ofcontrolling a process in a semiconductor processing chamber includes thesteps of flowing a first gas into an internal chamber of a gas manifoldand thence through apertures of the manifold toward a semiconductorwafer in the processing chamber, controlling an ultraviolet light sourceto illuminate the first gas within the gas manifold with ultravioletlight, wherein the ultraviolet light interacts with the first gas toproduce a second gas which comprises a non-ionic species, and flowingthe second gas through the apertures toward the semiconductor wafer. Themethod may further include stopping the flowing of the second gas bycontrolling the ultraviolet light source to stop illuminating the firstgas within the gas manifold. The method may also include heating thewafer by shining radiant energy on the wafer through the gas manifold.

An advantage of the invention is that it provides a wafer processingmethod and apparatus for producing highly reactive chemical species,including atomic species, from less dangerous, less reactive, andlonger-lived precursors. A further advantage of the invention is thatthe process does not produce ionic species, and therefore reduces therisk of damaging the semiconductor devices being formed on the waferwith such species.

Many of the reactive species formed according to the invention areshort-lived, and therefore do not pose a disposal or storage problem.The short-lived species can be produced and delivered to the surface ofa wafer in large enough quantities to enable faster processing. Bymultiply reflecting the UV light within the gas manifold, the precursorgas species is exposed to a higher intensity of UV radiation than wouldotherwise be available from the same source. This produces greaterquantities of reactive product gas species in less time than withsystems that do not employ multiple reflections. When processing withshort-lived species according to the invention, turning the ultravioletlight on and off starts and stops the flow of the reactive species tothe wafer in much shorter time periods than could be achieved with priorart systems, which feature allows for precise process control and rapidswitching between processes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view in partial section of a portion of a rapidthermal processing chamber according to the invention.

FIG. 2 is a view in partial section through line 2—2 of FIG. 1.

FIG. 3 is a partial section view similar to FIG. 2 illustrating anotherembodiment of a gas manifold assembly according to the invention.

FIG. 4 is a partial section view similar to FIGS. 2 and 3 thatillustrates a third embodiment of a gas manifold assembly.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, an rapid thermal process chamber 2 includes aquartz cylinder 4 supporting an edge ring 6, which in turn supports asemiconductor wafer 8 along its peripheral edge. It will be understoodthat the drawings are not to scale, but instead are drawn to bestillustrate the features of the invention. Cylinder 4 is rotatablysupported from the walls of process chamber 2 by a bearing assembly 10.Magnets 12, which are mounted on cylinder 4, have magnetic fields thatextend through the walls of process chamber 2 and that couple to magnets14 mounted on a rotatably driven drive ring 16. Rotating drive ring 16causes cylinder 4 and wafer 8 to rotate. The magnetic couplingeliminates the need for a vacuum sealed drive assembly.

Referring now also to FIG. 2, a gas manifold assembly 17 is positioneddirectly above wafer 8. Gas manifold assembly 17 includes a transparent,substantially cylindrically-shaped, fused quartz window 18. On anopposite side of window 18, outside of process chamber 2, is a lamparray 20 that heats wafer 8 with radiant energy. In the embodimentillustrated in FIGS. 1 and 2, gas manifold assembly 17 is held by lamparray 20 with tabs (not shown). An o-ring 19 provides a seal betweenwindow 18 and a wall of process chamber 2. Other arrangements can beemployed to hold gas manifold assembly 17 between lamp array 20 andwafer 8.

Window 18 includes a bottom pane 22 and a top pane 24 that are joined attheir peripheral edges by a window side wall 26. Panes 22, 24 areseparated by a small gap to provide an internal chamber 28 therebetween.Two posts 27 located near the center of window 18 provide additionalstructural support between panes 22, 24.

A process gas source 29 is coupled to a gas inlet 30 (not shown inFIG. 1) in window side wall 26. A process gas 32 flows into internalchamber 28 through inlet 30. Although FIG. 2 illustrates an embodimentwith a single gas inlet 30, window 18 can include more than one gasinlet 30. Thirty-six (36) small channels 34 each extend through bottompane 22. Process gas 32 flows out from internal chamber 28, throughchannels 34, at right angles toward wafer surface 36. Process gas 32becomes evenly distributed across wafer surface 36 when wafer is rotatedby the magnetic coupling to drive ring 16.

Gas manifold assembly 17 also includes a metal ring 38 substantiallysurrounding window side wall 26. Metal ring 38 has a high-finishreflective surface 40 facing the outside of window side wall 26 andfacing internal chamber 28. A slot 31 is provided in metal ring 38 forgas inlet 30. Metal ring 38 also includes an opening 42 through whichultra-violet (UV) light 44 produced by a UV light source 46 is directedthrough a window region 48 of window side wall 26 into internal chamber28. Window region 48 includes flat faces 50, 52 and is thinner than therest of window side wall 26.

UV light source 46 can be employed with optical elements 54 to direct UVlight 44 to shine onto window region 48. In the described embodiment,optical elements 54 include a rectangular-shaped stainless steel tube 60connecting between UV light source 46 and metal ring 38. Tube 60 has ahigh-finish inner reflecting surface 62 that directs UV light 44 throughwindow region 48 into internal chamber 28 substantially in a plane thatis parallel to panes 22, 24 and also parallel to wafer 8. UV light 44enters internal chamber 28 at a variety of angles within that plane. Asshown in FIG. 2, UV light 44 entering internal chamber 28 undergoesmultiple reflections (e.g., 44′, 44″, 44′″) from reflective surface 40,changing direction and path with each reflection. UV light 44 can passthrough window 18 more than one time or even several times due to thereflections from reflective surface 40.

UV light 44 can transform process gas 32, which may be a precursor gasspecies, into a different and more reactive product species. Themultiple reflections tend to increase the interactions with molecules ofprocess gas 32 within internal chamber 28, thereby increasing theproduction of the product species. The precursors may be less toxic,less unstable, or less corrosive than the product species, and thereforeeasier to store and handle. For example,

N₂O + υ --> NO + O (nitric oxide) 2O₂ + υ --> O₃ + O (ozone) CF₂Cl₂ +υ --> Cl + CF₂Cl (atomic chlorine) N₂ + υ --> N + N (atomic nitrogen)CF₄ + υ --> F + CF₃ (atomic fluorine).

In addition, the invention can be employed to make other atomic species,such as atomic oxygen and atomic hydrogen, and to make other molecularspecies. The process makes the product species without making any ionicspecies. Although the product species are typically short-lived, many ofthem having a half-life of about a minute or less, significantquantities of the product species flow through channels 34 onto wafersurface 36.

When the product species is a highly reactive species that dissipatesquickly, reactions on wafer surface 36 can be turned on or off rapidlyby turning UV light 44 on or off using a controller 56. Controller 56may include an electronic switch 56A coupled directly to UV light source46, or the electronic switch 56A may be coupled to a physical switchthat forms part of optics 54, for example, a rotatable mirror (notshown) interposed in the path of UV light 44 entering window 18.

UV light source 46 can include any UV light source producing UV light ofa wavelength and intensity useful for producing one or more selectedspecies for a selected process. UV light source 46 may include a UVlamp, a mercury (Hg) vapor discharge lamp, or a UV laser. Some UV laserscan be tuned to produce different wavelengths of light, which can beused to create different product species from different precursor gases.In general, one would use a wavelength tuned to maximize the productionof a desired reactive product species from a selected precursor gas. Atuning circuit 56B may be included in controller 56. The rate at whichthe reactive product species is produced and delivered to surface 36 ofwafer 8 depends on several factors, including the intensity of UV light44 within internal chamber 28, the dwell time of process gas 32 withininternal chamber 28, the gas flow rate and the half-life of the reactivespecies. In general, process parameters would be set empirically.

In the embodiment illustrated in FIGS. 1 and 2, window 18 is formed ofclear fused quartz, for example, NSG OZ or GE 214. Window side wall 26has an outer diameter of about 13.68 inches (347 mm) and a thickness ofabout 0.5 inch (12.6 mm). Bottom pane 22 is about 0.08 inch (2 mm)thick, top pane 24 is about 0.08 inch (2 mm) thick, and gap 28 is about0.08 inch (2 mm). Window area 48 has a width along window side wall 26of about 1.6 inches (40 mm) and a thickness of about 0.25 inch (8.2 mm).Channels 34, which each have a diameter of about 0.062 inch (1.6 mm) arearrayed on three equally spaced diagonals of window 18 on six concentricbolt circles having diameters of 1.732 inches (44 mm), 3.465 inches (88mm), 4.221 inches (107 mm), 6.063 inches (153 mm), 6.933 inches (176mm), and 8.666 inches (220 mm). Support posts each have a diameter ofabout 0.08 inches (2 mm) and are positioned on a 0.84 inch (21 mm) boltcircle. Gas feed-through 30 has a 0.078 inch (2 mm) diameter centralchannel. Metal ring 38 is made of stainless steel with a high finishinner reflecting surface 40. Wafer 16 is positioned about 0.15-0.3inches (4-8 mm) below window 18.

UV light source 46 and optical elements 54 will typically be locatedoutside of process chamber 10, where they can be serviced easily and beprotected from the harsh processing environment. Optical elements 54 caninclude any suitable means or combination of means to direct UV light 44from UV light source 46 into internal chamber 28, for example, opticfiber elements, lenses, fixed and movable mirrors, windows and the like.Optical elements 54 may be eliminated altogether if a beam of UV light44 can be made to shine directly into window area 48.

In another embodiment of a gas manifold assembly 102, illustrated inFIG. 3, a metallic coating 138 on a window side wall 126 provides areflective surface 140. Metallic coating 138 may be deposited directlyon window, for example, by evaporative deposition, sputter deposition,or any other metal coating technique. Optical elements 154 in thisembodiment include a fiber optic element 160, which directs a beam of UVlight 144 from a tunable laser UV light source 146 through an aperture170 in metallic coating 138. The beam is directed along a non-diagonalchord 119 into window 118 to increase the reflections and interactionswith precursor gas molecules within internal chamber 128.

Referring now to FIG. 4, another embodiment of a gas manifold assembly202 includes a pattern of apertures 234 in a bottom pane 222 of window218 that is similar to the pattern described above with reference toFIG. 2. A gas inlet 230 permits a flow of process gas into window 218.In this embodiment, a metal coating 238 provides a reflective surface240 on an inside surface of a window side wall 226. An aperture 270 inreflective surface 240 permits UV light 244 to enter internal window 218through a fiber optic coupling 260. This embodiment also includes alight deflecting optical device 274 that directs UV light 244 inoff-diagonal directions to increase the reflections within internalchamber 228. Light deflecting optical device 274 can be a prism, afresnel lens or the like. A metal ring 276 substantially surroundingwindow 218 can help to hold window 218 in position. Metal ring 276 mayhave a light absorbing interior coating to help stop stray UV light fromleaking out from the areas of gas inlet 230 and fiber optic fitting 260.

Gas manifold assemblies can be made according to the invention withdimensions and materials other than those employed with the describedembodiments. The number of channels in the bottom pane of the window andthe arrangement of the channels can be changed to suit the size andshape of the work piece toward which the reactive process gas isdirected.

Other embodiments are within the scope of the claims.

What is claimed is:
 1. A method of processing a semiconductor wafer in asemiconductor process chamber, comprising: providing a flow of aprecursor gas species into a gas manifold; illuminating the precursorgas species in the gas manifold with light, wherein the light travels indirections substantially parallel to the wafer and interacts with theprecursor gas species to create a product gas species; and flowing theproduct gas species through a plurality of apertures of the gas manifoldtowards the wafer in the processing chamber.
 2. The method of claim 1,wherein illuminating includes directing the light into the gas manifold,the light undergoing multiple reflections off a reflective surface ofthe gas manifold.
 3. The method of claim 1, wherein the gas manifoldcomprises a transparent window, the method further comprising heatingthe wafer by shining radiant energy from a heat lamp array through thewindow.
 4. The method of claim 1, wherein the product gas speciescomprises nitric oxide.
 5. The method of claim 1, wherein the productgas species comprises ozone.
 6. The method of claim 1, wherein theproduct gas species comprises an atomic species.
 7. The method of claim1, further including controlling the processing by controlling theilluminating.
 8. The method of claim 1, wherein the product gas speciescomprises a gas species having a half-life of about a minute or less. 9.A method of controlling a process in a semiconductor processing chamber,comprising: flowing a first gas into an internal chamber of a gasmanifold and thence through apertures of the gas manifold toward asemiconductor wafer in the processing chamber; controlling a lightsource to illuminate the first gas within the gas manifold with light,wherein the light travels in directions substantially parallel to thewafer and interacts with the first gas to create a second gas thatincludes a non-ionic species; flowing the second gas through theapertures toward the semiconductor wafer.
 10. The method of claim 9,further comprising stopping the flowing of the second gas by controllingthe light source to stop illuminating the first gas within the gasmanifold.
 11. The method of claim 9, wherein illuminating the first gasincludes directing the light into the gas manifold, the light undergoingmultiple reflections from a reflective surface of the gas manifold. 12.The method of claim 9, wherein the non-ionic species comprises an atomicspecies.
 13. The method of claim 9, further comprising heating the waferby shining radiant energy on the wafer through the gas manifold.